The present invention is concerned with a method and apparatus for the separation, depletion, or enrichment of atoms or molecules, and is particularly concerned with the separation, depletion, or enrichment of a preselected atom or molecule from a mixture containing the preselected atom or molecule and at least one other or molecule having different mass, by transport through a solid electrolyte.
Various methods have been previously suggested for separating and enriching molecules such as isotopes of the same element. Included in such prior suggested methods are several physical processes such as gas diffusion and centrifical separation. These physical methods; however, require extremely large equipment along with a large capital outlay which in turn renders the products very expensive.
In addition, certain chemical methods for separating molecules have been suggested. For instance, A. K. Brewer et al in J. Research Nat. Bur. Standards, 38, 137 (1947) and S. L. Mardrosky et al, IBID, 38, 185 (1947) suggested separation by electromigration in aqueous solution. However, these electromigration methods were not very efficient since the migration of the isotopic ions was disturbed by the migration of counter ions traveling in the opposite direction. In addition, the effect of separation obtained by difference in masses of the isotopes is reduced because of hydration of the ions during migration. Therefore, separation and enrichment of isotopes on a commercial basis has not been feasible with such methods.
In order to overcome the problem of hydration of ions during such migration, A. Klem et al, Zeitschrift Fur Naturforschung 16a, 685 (1961) suggested the use of fused salts for the separation and enrichment of ions. However, this method suffered from the disadvantage that very high temperatures are needed to maintain salt in the fused state.
Still a further suggested method involved a use of ion exchange granular resins. In such method, the ions to be separated are absorbed by the resins from a liquid through an ion exchange reaction and thereafter migrate in the resin by virtue of the potential applied thereto. Such methods, however, proved to be very inefficient and not very practical.
Moreover, an electromigration separation method has been suggested which employs a membrane of regenerated cellulose or collodion (for instance, see U.S. Pat. No. 2,989,457). Such a proposed method, however, suffers from the disadvantage that the regenerated cellulose and collodion do not possess the characteristics for transmitting only cations selectively, and counterions also migrate through the membrane. Moreover, these membranes are not very resistant to various chemicals with whch they must come in contact with during use.
A still further suggested method for separating molecules is the use of two separate solutions while employing an ion exchange resin material as suggested by Seko et al in U.S. Pat. No. 3,425,924. However, this method suffers from a number of disadvantages including the necessity to use a plurality of solutions of different ions and thereby contributing to the complexity of the process. Another disadvantage of such an ion exchange method is its primary dependence upon the surface properties of the resin. Although some improvement in volume utilization can be achieved by using relatively small resin grains, the separation depends upon a surface effect rather than a volume effect. Accordingly, scaling up of the process to a large size is much less efficient than when a volume effect is utilized as in the present invention.
Accordingly, continuing work is being done to provide improved methods for separation, depletion, and/or enrichment of atoms and molecules and particularly isotopes of the same element, which processes can be used on a large commercial scale. An object of the present invention is to provide a method which enables the concentration of preselected atoms or molecules to be changed (e.g.-enrichment, depletion, or separation) quasi-continuously and economically within a commercial scale operation. Another object of the present invention is to provide a method which is sufficiently versatile so as to be applicable to all kinds of elements except possibly the rare gas elements which are difficult to prepare as ions. A further object of the present invention is to provide a process which is suitable for separating molecules or isotopes of an element in ionic form which differ from each other only slightly in mass.
A further object of the present invention is to provide a process for the enrichment or depletion of molecules which is efficient, and particularly, more efficient than, for instance, the prior liquid electrolysis processes. A further object of the present invention is to provide a process which does not require excessive amounts of energy to effect the desired enrichment.
A further object of the present invention is to provide a process which does not require the expenditure of large amounts of money nor complex and large equipment.